#include<stdio.h>
#include<math.h>
int main(){
	double m,ls=1,s=0,s1=1;
	double cnt=1;
	scanf("%lf",&m);
	s=m;
	while(fabs(m/s1)>=1e-4)
	{
		cnt++;
		ls=-ls;
		s1*=cnt;
		m*=m;
		s=s+ls*(m/s1);
	}
	printf("%.2f\n",s);
return 0;
}